Impact printer

ABSTRACT

An impact line printer is provided with a character drum which has characters such as letters and numerals on the peripheral surface thereof and printing hammers in opposite to the character drum, wherein a printing paper is passed between the character drum and the printing hammers. The printer is further provided with a driven shaft on which is mounted frictional discs. Wheel members are provided, each of which is opposed to and normally spaced apart from each of the frictional discs. The wheel members are selectively brought into contact with the frictional discs to actuate selected printing hammers to effect printing on the printing paper. The printing hammers on normally biased for example by means of spring to keep away from the character drum.

United States Patent 1 Nishikawa et a1.

[451 Dec. 30, 1975 [54] IMPACT PRINTER [73] Assignee: Canon Kabushiki Kaisha, Tokyo,

Japan 22 Filed: July 10,1974

211 Appl. No: 487,370

[30] Foreign Application Priority Data July 20, 1973 Japan 48-82032 July 13, 1973 Japan 48-83478[U] [52] U.S. Cl l01/93.3; 101/93.31 [51] Int. Cl. B41J 9/32 [58] Field of Search 101/93.29, 93.36, 93.48; 192/48.2, 84 AA, 84 B, 84 C [56] References Cited UNITED STATES PATENTS 2,039,714 5/1936 Fuller 192/84 C 3,477,365 11/1969 Nyman 101/93.34 X 3,704,770 12/1972 Spencer r. 192/84 A X 3,795,190 3/1974 Wallace 101/91 X 3,854,562 12/1974 Wilczewski l92/84C OTHER PUBLICATIONS IBM Technical Disclosure Bulletin, Point Hammer Drive, Wanlemueller, Vol. 11, No. 11, Apr. 1969, p. 1609.

Primary Examiner-Edgar S. Burr Assistant Examiner-E. M. Coven Attorney, Agent, or Firm-Fitzpatrick, Cella, Harper & Scinto [57] ABSTRACT An impact line printer is provided with a character drum which has characters such as letters and numerals on the peripheral surface thereof and printing hammers in opposite to the character drum, wherein a printing paper is passed between the character drum and the printing hammers. The printer is further provided with a driven shaft on which is mounted frictional discs. Wheel members are provided, each of which is opposed to and normally spaced apart from each of the frictional discs. The wheel members are selectively brought into contact with the frictional discs to actuate selected printing hammers to effect printing on the printing paper. The printing hammers on normally biased for example by means of spring to keep away from the character drum.

16 Claims, 13 Drawing Figures U.S. Patent Dec. 30, 1975 Sheet 2 of5 3,929,067

FIG. 4

FIG.

US. Patent Dec. 30, 1975 Sheet 3 of5 3,929,067

US. Patent Dec. 30, 1975 Sheet 4 of5 3,929,067

US. Patent Dec. 30, 1975 SheetSofS 3,929,067

IMPACT PRINTER BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention, in general, relates to an impact printer and more particularly to an improved impact printer which is capable of obtaining sufficient impact force with a compact structure utilizing electromagnetic solenoids.

2. Description of the Prior Art The prior art in the line of art toward which the present invention is orientated includes the so-called impact printer systems in which printing paper having a carbon ribbon, placed thereon or pressure-sensitive printing paper is set in opposition to a circular drum on which characters are arranged in lines, and then the printing paper is hit against the characters on the drum by means of a hammer to thereby effect printing on said printing paper. In the known impact printers, particularly impact line printers, the characters to be printed are suitably arranged on the peripheral surface of a revolvable character drum and printing paper moving transversely to the axis of said type drum is placed adjacent to the peripheral surface of the drum, while an ink ribbon impregnated with ink is positioned in opposition to the face of said printing paper opposite from the side opposed to the drum, and then the printing paper is hit by one of the printing hammers against the desired one of the characters on the peripheral surface of the character drum to obtain on said printing paper the printed letter or figure corresponding to the character hit by said hammer. The printing hammers are arranged parallel to the axis of the type drum and the characters set circumferentially on said drum surface are grouped for each of the printing hammers, each said group comprising characters different from those of the other groups, so that any desired character may be printed on a desired line by suitably selecting a hammer and a corresponding group of characters. However, since each of said hammers is adapted to be driven directly by an electromagnetic solenoid, it was necessary to use a large-capacity and largesize solenoid, and for this reason, the known types of line printers have been mostly used for output printing in largesized electronic computing or data processing machines. Recently, however, printing apparatuses have come to be used popularly in small-sized machines and equipments such as desk-top electronic computers, and naturally, a strong request has been voiced for smallsized line printers.

However, the effort for miniaturizing the line printers has encountered many difficult problems. For instance, miniaturization of the electromagnetic solenoids used for hammer driving was attended by great technical difficulties, and also, even if the hammers could be driven by small-sized electromagnetic solenoids, thgre could hardly be obtained sufficient percussive force for practicing printing in a desired way.

As a significant attempt for solution to these problems, there has been proposed a small-sized line printer system equipped with a so-called trigger type hammer driving mechanism, in which, as shown in US. Pat. Nos. 3,598,046, 3,623,428 and 3,623,429, the hammer driving force is obtained from a cam shaft by incorporating a hammer driving mechanism, with a small-output electromagnetic solenoid being adapted to serve as trigger, within the sphere of rotation of the cam shaft which is constantly rotated by an electric motor.

Although this system is, on one hand, capable of offering a small-sized and very efficient line printer, it has, on the other hand, some serious problems such as mentioned below. That is, considerable noise develops when incorporating the hammer driving mechanism in the sphere of rotation of the cam shaft, and also, in certain positions of rotation of the cam shaft, there arises a time lag from the time when the hammer driving mechanism is adapted to the cam shaft until the hammers are actually driven, resulting in elongated responding time and hence low printing speed. This system also has the problems of poor economy and low reliability due to the complicated mechanical construction and reduced durability owing to impact given when adapting the hammer driving mechanism within the sphere of rotation of the cam shaft.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an impact printer which is exceedingly small in size and weight, simple in structure, and low in manufacturing cost. v

Another object of the present invention is to provide an impact printer which is of the size and shape best suitable for adaption in a small-sized desk-top electronic computing machine.

Still another object of the present invention is to provide an impact printer which is quick in response, low in operating sound, and capable of high speed printing.

Yet another object of the present invention is to provide an impact printer which can be easily reduced in size as the printing hammers can be arranged closely in a line when the device is adapted as a line printer.

A further object of the present invention is to provide an impact printer in which an electromagnetic interface controlled by an electric signal is adopted when driving the printing hammers with rotative energy accumulated in a flywheel.

An additional object of the present invention is to provide an impact printer in whichelectromagnetic clutch assemblies are used to serve as electromagnetic interfaces for transmitting the rotative energy accumulated in the fly-wheel to the respective printing hammers.

It is still another object of the present invention to provide an impact printer in which the electromagnetic clutch assemblies adapted for driving the respective printing hammers are constructedvery simply and in small size.

It is yet another object of the present invention to provide an impact printer in which a mechanism operable at high efficiency and with small power consumption is employed for each electromagnetic clutch as- .g embly for driving each printing hammer.

;The other objects of the present invention will become apparent from the consideration of the following detailed description of the embodiments of the invention and will be definitely stated in the appended claims. Also, many advantages and benefits which are not mentioned in this specification will readily suggest themselves to those skilled in the art when practicing the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of an impact printer according to a preferred embodiment of the present invention;

FIG. 2 is an exploded perspective view of an electromagnetic clutch assembly which constitutes a driving part of a printing hammer shown in FIG. 1;

FIG. 3 is a perspective view of the rotative member of FIG. 2 and a magnet coil assembly as taken from a different angle;

FIG. 4 is a longitudinal sectional view of an array of electromagnetic clutches constituting a driving mechanism of the printing hammers;

FIG. 5 is a diagrammatic sketch illustrating the operation of the electromagnetic clutch assembly shown in FIG. 4;

FIGS. 6A, 6A, 6B, 6B, 6C, and 6C illustrate the operations of a printing hammer of FIG. 1 and the electromagnetic clutch assembly constituting a driving part for said hammer;

FIG. 7 is a perspective view of an impact printer according to another embodiment of the present invention; and

FIG. 8 is a perspective view of an impact printer according to still another embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring first to FIG. 1, it will be seen that groups or lines of characters 4 are arranged regularly on the peripheral surface of a character drum 2 which is rotated by a suitable means not shown, and a printing sheet 8 is disposed close to the peripheral surface of the character drum such that the printing sheet is movable transversely to the axis of the drum 2. Also, an ink ribbon 10 imgregnated with ink is positioned opposite to the face of said printing sheet opposite from its side opposed to the character drum 2. The printing sheet 8 is hit through said ink ribbon 10 by the head portion 14 of one of the hammers 12 against any desired one of the characters 4 on the peripheral surface of the character drum 2, whereby a letter or figure corresponding to the character hit by said heat portion 14 of the particular hammer 12 is printed on the printing sheet 8.

The hammers 12 are arranged in line parallel to the axis 6 of the character drum 2, and each line of characters 4 arranged on the peripheral surface of the revolvable character drum 2 constitutes a group composed of the characters different from those of the other groups. It is thus possible to obtain desired printed letters (figures numerals and the like) on a desired line by suitably selecting and combining the printing hammers l2 and the characters in each group of characters 4.

The printing hammers 12 are retained slidable in their longitudinal direction by a retainer member 16 and are also elastically pulled in the direction opposite from the character drum 2 by springs I8. At the portion 20 of each hammer 12 opposite from its head portion 14 is provided a rack 22 which is meshed with the teeth 24 of a corresponding rotatable wheel member 26. The teeth 24 are formed along a part of the periphery of each the wheel member 26.

The wheel members 26 are turned in the direction of the arrow a by a motor 28. That is, the driving force of the shaft 32 stored in a fly wheel is transmitted through electromagnetic clutch means (not shown) to the respective wheel members 26 to let them turn in the direction of the arrow a, causing the hammers 12 engaged with the respective wheel members 26 through rack-and-teeth engagement to move in the direction of the arrow b. A control signal from a control unit, not shown, is inputted through a signal line 34 to each of said electromagnetic clutch means to control it at regulated timing and duration. That is, any one of the electromagnetic clutch means is operated to actuate the desired one of the hammers 12 in the direction of the arrow b at such timing that the desired character in the corresponding line of characters 4 on the peripheral surface of the character drum 2 will be brought to the position for printing on the printing sheet 8, and then the head portion 14 of the particular hammer I2 is hit against the desired character through the ink ribbon 10 and sheet 8 to thereby obtain the printed letter of figure of the particular character on a desired line on the printing sheet 8.

FIG. 2 shows a perspective exploded view of one of the above-said electromagnetic clutch assemblies. Rotative energy is accumulated in the fly wheel 30 on the driving shaft 32 of the electric motor 28 to give a large rotative force to each friction plate 36 made of a magnetic material such as iron, which is axially mounted on the shaft 32. A wheel member 26 made of a magnetic material such as iron is mounted slidably in opposite to each of the friction plate 36 and rotatably on the shaft 32 through a bearing 38, the member 26 having on its side opposed to said friction plate 36 an annular hollow portion 40 such as shown in FIG. 3, and an annular magnet coil 42 is disposed loosely in the hollow portion 40, with the lead wire 44 of the magnet coil 42 being extended out from an opening 46 in said member 26 and connected to a power source. Reference numeral 48 indicates a radial leaf spring interposed between the magnet coil 42 and the friction plate 36 for securing the magnet coil against looseness and for regulating abutment between the wheel member 26 and the friction plate 36. Numeral S0 is a separator plate adapted for separating the electromagnetic clutch assembly from the adjoining one.

Being constructed as described above, the electromagnetic clutch assemblies are arranged in juxtaposition corresponding to the respective hammers 12 as shown by a longitudinal sectional drawing in FIG. 4.

Each of the wheel members 26 is energized upon connection of said magnet coil 42 to power through the lead wire 44 to produce a magnetic attraction force between the member 26 and the friction plate 36 to let them press against each other against the opposing force of the leaf spring 48 as shown in FIG. 5, thereby transmitting the rotative force of the shaft 32 to the wheel member 26 through the friction plate 36.

As said before, each of the wheel members 26 has provided along a part of its outer periphery a toothed section 24 which meshes with the rack 22 provided on the associated printing hammer 12 which is constantly pressed by a spring 18 in the direction opposite from the character drum 2, and each printing hammer I2 is retained slidably in its longitudinal direction by a retainer member 16. Thus, when said wheel member 26 receives the rotative force through the friction plate 36 upon energization of the magnet coil 42, the associated printing hammer 12 also receives the driving force through engagement of said toothed section 24 and rack 22 and is thereby urged to move in the direction of the arrow [1 to hit one of the characters 4 on the character drum 2 through the ink ribbon l and printing sheet 8 to thereby print the letter or figure corresponding to the hit character on the printing sheet 8.

Now, the operation of each just-described electromagnetic clutch assembly and associated printing hammer 12 are discussed with reference to the illustrative drawings of FIG. 6 in which (A), (B) and (C) are sectional side views of the printing mechanism including the electromagnetic assemblies and printing hammers, and (A'), (B) and (C') are sectional views of the electromagnetic clutch assemblies taken along the line A'A of (A), (B) and (C).

FIGS. 6(A) and (A') show a condition where the magnet coil 42 is not connected to power. Under this condition, since both magnet coil 42 andthe wheel member 26 remain inoperative, no pressing force'acts between said wheel member 26 and the friction plate 36 which is constantly rotating in the direction of the arrow a, so that the rotative force of the shaft 32 is not transmitted to the wheel member 26 and hence the member 26 is urged to turn clockwise, that is, in the direction opposite to the direction of rotation of the friction plate 42 owing to the direction of rotation of the friction plate 42 owing to the force of the spring 18 which is pulling the printing hammer 12 in the direction of the arrow b. Here, if the magnet coil 42 is connected to power, the wheel member 26 is energized to attract the friction plate 36 so that they are securely attached to each other as shown in FIG. 6(B), and consequently, the rotative force of the friction plate 36 in the direction of the arrow a is transmitted to the wheel member 26 due to the friction force developed between the wheel member 26 and the friction plate 36 by the pressed attachment, causing wheel member 26 to turn clockwise, that is, in the direction of the arrow a against the opposing pulling forceof the spring 18 that is given indirectly through engagement of the rack 22 and teeth 24. As shown in FIG. 6(B), the rotative force of the wheel member 26 is transmitted to the printing hammer 12 through the meshed teeth 24 and rack 22 to drive the hammer 12in the direction of the arrow b so that the'hammer head 14 hits against a character 4 on the character drum 2 through the ink ribbon l0 and printing sheet 8 interposed therebetween. The range of turning motion of the wheel member 26 is restricted by the peripheral length of the opening 46 through which the leadwire 44 of the magnet coil 42 extends out, so the entire arrangement is made such that the necessary printing operations can be accomplished with in the range of turning motion defined by the peripheral length of the opening 46 and that upon completion of such printing operations, power to the magnet coil 42 is-disconnected. Upon disconnection of power to the magnet coil 42, the coupling force between the wheel member 26 and the friction plate 36 dies away and hence no rotative force is transmitted from the friction plate 36 to the wheel member 26, so that the wheel member 26 and printing hammer 12 are returned to their original positions by the force of spring 18 acting in the direction of the arrow b as shown in FIGS. 6(C) a'nd (C').

The above-described operations constitute one printing cycle. In this cycle, it is to be noted that there is formed a magnetic circuit which suffers little'leakage of magnetic line of force, so that very'strong and secure magnetic coupling of the friction plate 36 and the wheel member 26 can be obtained with a small electric current and a small-sized magnet coil 42 as shown in FIG. 5. v

FIG. 7 is a perspective view of an impact printer according to another embodiment of the present invention. In this embodiment, each printing hammer 12 is provided integral with the corresponding wheel member 26 so that when the'electromagnetic clutch assembly is operated in accordance with a control signal inputted through a signal line 34, rotative force is transmitted to the wheel member 26 through a friction plate 36 axially mounted on the shaft 32 driven to rotate in the direction of the arrow a by a motor 28, causing said printing hammer 12 to turn in the direction of the arrow a against the force of spring 52 so that the hammer head 14 hits a character 4 on the character drum I 2 through an ink ribbon l0 and a printing sheet 8 to embodiment of FIG. 1, and they are very compact and can operate at high efficiency.

FIG. 8 shows, in perspective, the mechanism of an impact printer according to still another embodiment of the present invention. In this embodiment, each of the printing hammers l2 given an urge to move in the direction opposite to the direction of the arrow a by a spring 18 but inhibited in such movement by a block 62 is provided integral with a hammer base 60 which is rotatably supported on a shaft member 58 disposed parallel to the driving shaft 32 and which has a toothed section 56 meshed with the corresponding toothed portion 24 formed at a part of the outer periphery of the corresponding wheel member 26 which receives the rotative force through an electromagnetic clutch assembly similar to that used in the embodiment of FIG. 1 from the driving shaft 32 rotated in the direction of the arrow p by an electric motor 28 in accordance with a control signal from a signal line 34. Thus, when the particular clutch assembly is actuated upon receiving a control signal inputted through an associated signal line 34, rotative force is transmitted to the association wheel member 26 through a friction plate axially mounted on the driving shaft 32 which is rotated in the direction of the arrow p by electric motor 28, causing the related hammer base 60 to turn in the direction of the arrow a against the force of spring 18 through the meshed engagement of the teeth 56 with the corresponding teeth 24 on the wheel member 26, so that the hammer head 14 hits a character 4 on the character drum 2 through an ink ribbon l0 and a printing sheet 8 to print on said sheet 8 a letter or figure corresponding to the character hit by the hammer head 14.

In each of the foregoing embodiments, a fly wheel 30 is provided for storing rotative energy when the driving shaft 32 is rotated by the motor 28, so as to give a large rotative force to the driving shaft 32.

Thus, according to the present invention featuring the above-described novel arrangements, it is possible to obtain a line printer which is extremely compact and small-sized in structure, quiet in running, quick in response to signal, high in printing speed, simple inmechanism and low in manufacturing cost. I

While the present invention has been described in detail by way of some preferred embodiments thereof,

it will be understood that such description of the preferred embodiments is merely illustrative and does not cover the entire details of the invention and the combination and arrangement of the component parts can be varied in various other ways without departing from the spirit and scope of the present invention which is only defined by the appended claims.

We claim:

1. An impact printer comprising:

a type base carrying at least one group of typing characters, each of which being selectively faced toward printing paper;

a drive shaft having a driving force continuously applied thereto;

a friction disc mounted on said drive shaft corresponding to each said group of typing characters;

a wheel member disposed coaxially with and in facing relationship with respect to each said friction disc, said wheel member being rotatable relative to said friction disc;

an energizable magnet coil means for establishing, when energized, driving engagement between said wheel member and said friction disc by the magnetic force thereof, said magnetic coil being free from the rotation of said friction disc and said wheel member;

a printing hammer means for impacting a selected one of said typing characters through the recording paper;

means for urging said printing hammer means away from said type base; and

means for transmitting the driving force, applied to said wheel member through said friction disc, to said printing hammer means, thereby enabling said printing hammer means to overcome the urging force of said urging means and impact a selected typing character when said coil means is energized.

2. A printer according to claim 1, wherein said transmitting means comprises, a gear provided on a portion of a peripheral surface of said wheel member, and a rack gear provided on a portion of said printing hammer means and being engageable with said gear.

3. A printer according to claim 1, wherein said transmission means comprises an arm directly connecting said wheel member and said printing hammer means.

4. A printer according to claim 1, wherein said transmission means comprises, a gear provided on a portion of a peripheral surface of said wheel member, a hammer base rotatably supported on a shaft disposed in parallel with said drive shaft, said hammer base having a gear engageable with said gear provided on said wheel member and an arm for fixing said printing hammer on said hammer means base.

5. An impact printer comprising:

a type base carrying at least one group of typing characters, each of which being selectively faced toward printing paper;

a drive shaft having a driving force continuously applied thereto;

a friction disc mounted on said drive shaft corresponding to each said group of typing characters;

a wheel member disposed coaxially with and in facing relationship with respect to each said friction disc, said wheel member being rotatable relative to said friction disc and having an annular recess in the side thereof facing said friction disc;

annular energizable magnet coil means for establishing, when energized, driving engagement between said wheel member and said friction disc by the magnetic force thereof, said magnet coil means being loosely fitted within the recess of said wheel member;

a printing hammer means for impacting a selected one of said typing characters through the recording paper;

means for urging said printing hammer means away from said type base; and

means for transmitting the driving force, applied to said wheel member through said friction disc, to said printing hammer means, thereby enabling said printing hammer means to overcome the urging force of said urging means and impact a selected typing character when said coil means is energized.

6. A printer according to claim 5, wherein a plurality of said friction discs and a plurality of said wheel members are coaxially disposed, alternately.

7. A printer according to claim 5, wherein said wheel member is provided, on a peripheral wall thereof, with an opening through which a lead wire of the coil means extends.

8. A printer according to claim 5, further comprising, a resilient member disposed between said magnet coil means and said friction disc to urge them apart.

9. A printer according to claim 7, wherein said transmitting means comprises, a gear provided on a portion of a peripheral surface of said wheel member, and a rack gear provided on a portion of said printing hammer means and being engageable with said gear.

10. A printer according to claim 7, wherein said transmission meanscomprises, an arm directly connecting said wheel member and said printing hammer means.

11. A printer according to 'claim 8, wherein said transmission means comprises, a gear provided on a portion of a peripheral surface of said wheel member, a hammer base rotatably supported on a shaft disposed in parallel with said drive shaft, said hammer base having a gear engageable with said gear provided on said wheel member and an arm for fixing said printing hammer means on said hammer base.

12. An impact printer comprising:

a type drum carrying at least one line of typing characters, said type drum being rotatable about an axis thereof to selectively face one of the typing characters toward printing paper;

a drive shaft disposed in parallel with said type drum,

' said drive shaft having a driving force continuously applied thereto from a driving source;

a friction disc mounted on said drive shaft corresponding to said line of typing characters, said friction disc being continuously rotated;

a wheel member disposed rotatably and coaxially with respect to each said friction disc, said wheel member having an annular recess in the side thereof facing said friction disc;

annular energizable magnet coil means for establishing, when energized, driving engagement between said wheel member and said friction disc by the magnetic force'thereof, said magnet coil means being loosely fitted within the recess of said wheel member;

an opening provided on a peripheral surface of said wheel member to pass a lead wire therethrough for energizing'said magnet coil means;

a resilient member disposed between said magnet coil means and said friction disc to urge them apart,

a printing hammer means for impacting a selected one of said typing characters through the recording paper;

means for urging said printing hammer means away from said type base;

means for transmitting the driving force, applied to said wheel member through said friction disc, to said printing hammer means, thereby enabling said printing hammer means to overcome the urging force of said urging means and impact a selected typing character when said coil means is energized.

13. A printer according to claim 12, wherein said transmitting means comprises, a gear provided on a portion of a peripheral surface of said wheel member, and a rack gear provided on a portion of said printing hammer means and being engageable with said gear.

14. A printer according to claim 12, wherein said transmission means comprises, an arm directly connecting said wheel member and said printing hammer means.

15. A printer according to claim 12, wherein said transmission means comprises, a gear provided on a portion of a peripheral surface of said wheel member, a hammer base rotatably supported on a shaft disposed in parallel with said drive shaft, said hammer base having a gear engageable with said gear provided on said wheel member, and an arm for fixing said printing hammer means on said hammer base.

16. An impact printer comprising:

a type drum carrying a plurality of lines of typing characters, said type drum being rotatable about an axis thereof to selectively face desired typing characters toward printing paper;

a drive shaft disposed in parallel with said type drum, said drive shaft having a driving force continuously applied thereto from a driving force;

friction discs mounted on said drive shaft corresponding to the respective lines of the typing char- 10 acters, said friction discs being continuously rotated;

wheel members disposed coaxially with and in facing relationship with the respective friction discs, said wheel members being rotatable relatively to the respective friction discs, and each of said wheel members having an annular recess in the side thereof facing the corresponding friction disc;

a plurality of annular energizable magnet coil means for establishing, when energized, respective driving engagements between said wheel members and said friction discs by the magnetic force thereof, said magnet coil means being loosely fitted within the respective recesses of said wheel members;

openings provided in the peripheral surfaces of said wheel members, respectively, to pass lead wires therethrough for the respective magnet coil means;

resilient members disposed between each of said magnet coil means and the corresponding one of said friction discs to urge them apart;

first gears provided on portions of said wheel members, respectively;

hammer bases rotatably supported on a shaft which is disposed in parallel with said drive shaft, said hammer bases each having a second gear engageable with the corresponding one of said first gears on said wheel members;

printing hammers fixedly mounted on the respective hammer bases corresponding to the respective lines of typing characters, said printing hammers each impacting, when the corresponding coil means is energized, a selective one of the characters facing the printing paper through the printing paper by an impacting force applied thereto through the corresponding friction disc, wheel member, first gear, second gear and hammer base in the order named; and

means for urging said printing hammers away from said type bases, respectively. 

1. An impact printer comprising: a type base carrying at least one group of typing characters, each of which being selectively faced toward printing paper; a drive shaft having a driving force continuously applied thereto; a friction disc mounted on said drive shaft corresponding to each said group of typing characters; a wheel member disposed coaxially with and in facing relationship with respect to each said friction disc, said wheel member being rotatable relative to said friction disc; an energizable magnet coil means for establishing, when energized, driving engagement between said wheel member and said friction disc by the magnetic force thereof, said magnetic coil being free from the rotation of said friction disc and said wheel member; a printing hammer means for impacting a selected one of said typing characters through the recording paper; means for urging said printing hammer means away from said type base; and means for transmitting the driving force, applied to said wheel member through said friction disc, to said printing hammer means, thereby enabling said printing hammer means to overcome the urging force of said urging means and impact a selected typing character when said coil means is energized.
 2. A printer according to claim 1, wherein said transmitting means comprises, a gear provided on a portion of a peripheral surface of said wheel member, and a rack gear provided on a portion of said printing hammer means and being engageable with said gear.
 3. A printer according to claim 1, wherein said transmission means comprises an arm directly conNecting said wheel member and said printing hammer means.
 4. A printer according to claim 1, wherein said transmission means comprises, a gear provided on a portion of a peripheral surface of said wheel member, a hammer base rotatably supported on a shaft disposed in parallel with said drive shaft, said hammer base having a gear engageable with said gear provided on said wheel member and an arm for fixing said printing hammer on said hammer means base.
 5. An impact printer comprising: a type base carrying at least one group of typing characters, each of which being selectively faced toward printing paper; a drive shaft having a driving force continuously applied thereto; a friction disc mounted on said drive shaft corresponding to each said group of typing characters; a wheel member disposed coaxially with and in facing relationship with respect to each said friction disc, said wheel member being rotatable relative to said friction disc and having an annular recess in the side thereof facing said friction disc; annular energizable magnet coil means for establishing, when energized, driving engagement between said wheel member and said friction disc by the magnetic force thereof, said magnet coil means being loosely fitted within the recess of said wheel member; a printing hammer means for impacting a selected one of said typing characters through the recording paper; means for urging said printing hammer means away from said type base; and means for transmitting the driving force, applied to said wheel member through said friction disc, to said printing hammer means, thereby enabling said printing hammer means to overcome the urging force of said urging means and impact a selected typing character when said coil means is energized.
 6. A printer according to claim 5, wherein a plurality of said friction discs and a plurality of said wheel members are coaxially disposed, alternately.
 7. A printer according to claim 5, wherein said wheel member is provided, on a peripheral wall thereof, with an opening through which a lead wire of the coil means extends.
 8. A printer according to claim 5, further comprising, a resilient member disposed between said magnet coil means and said friction disc to urge them apart.
 9. A printer according to claim 7, wherein said transmitting means comprises, a gear provided on a portion of a peripheral surface of said wheel member, and a rack gear provided on a portion of said printing hammer means and being engageable with said gear.
 10. A printer according to claim 7, wherein said transmission means comprises, an arm directly connecting said wheel member and said printing hammer means.
 11. A printer according to claim 8, wherein said transmission means comprises, a gear provided on a portion of a peripheral surface of said wheel member, a hammer base rotatably supported on a shaft disposed in parallel with said drive shaft, said hammer base having a gear engageable with said gear provided on said wheel member and an arm for fixing said printing hammer means on said hammer base.
 12. An impact printer comprising: a type drum carrying at least one line of typing characters, said type drum being rotatable about an axis thereof to selectively face one of the typing characters toward printing paper; a drive shaft disposed in parallel with said type drum, said drive shaft having a driving force continuously applied thereto from a driving source; a friction disc mounted on said drive shaft corresponding to said line of typing characters, said friction disc being continuously rotated; a wheel member disposed rotatably and coaxially with respect to each said friction disc, said wheel member having an annular recess in the side thereof facing said friction disc; annular energizable magnet coil means for establishing, when energized, driving engagement between said wheel member and said friction disc by the magnetic force thereof, said magnet coil means being loosely fitTed within the recess of said wheel member; an opening provided on a peripheral surface of said wheel member to pass a lead wire therethrough for energizing said magnet coil means; a resilient member disposed between said magnet coil means and said friction disc to urge them apart, a printing hammer means for impacting a selected one of said typing characters through the recording paper; means for urging said printing hammer means away from said type base; means for transmitting the driving force, applied to said wheel member through said friction disc, to said printing hammer means, thereby enabling said printing hammer means to overcome the urging force of said urging means and impact a selected typing character when said coil means is energized.
 13. A printer according to claim 12, wherein said transmitting means comprises, a gear provided on a portion of a peripheral surface of said wheel member, and a rack gear provided on a portion of said printing hammer means and being engageable with said gear.
 14. A printer according to claim 12, wherein said transmission means comprises, an arm directly connecting said wheel member and said printing hammer means.
 15. A printer according to claim 12, wherein said transmission means comprises, a gear provided on a portion of a peripheral surface of said wheel member, a hammer base rotatably supported on a shaft disposed in parallel with said drive shaft, said hammer base having a gear engageable with said gear provided on said wheel member, and an arm for fixing said printing hammer means on said hammer base.
 16. An impact printer comprising: a type drum carrying a plurality of lines of typing characters, said type drum being rotatable about an axis thereof to selectively face desired typing characters toward printing paper; a drive shaft disposed in parallel with said type drum, said drive shaft having a driving force continuously applied thereto from a driving force; friction discs mounted on said drive shaft corresponding to the respective lines of the typing characters, said friction discs being continuously rotated; wheel members disposed coaxially with and in facing relationship with the respective friction discs, said wheel members being rotatable relatively to the respective friction discs, and each of said wheel members having an annular recess in the side thereof facing the corresponding friction disc; a plurality of annular energizable magnet coil means for establishing, when energized, respective driving engagements between said wheel members and said friction discs by the magnetic force thereof, said magnet coil means being loosely fitted within the respective recesses of said wheel members; openings provided in the peripheral surfaces of said wheel members, respectively, to pass lead wires therethrough for the respective magnet coil means; resilient members disposed between each of said magnet coil means and the corresponding one of said friction discs to urge them apart; first gears provided on portions of said wheel members, respectively; hammer bases rotatably supported on a shaft which is disposed in parallel with said drive shaft, said hammer bases each having a second gear engageable with the corresponding one of said first gears on said wheel members; printing hammers fixedly mounted on the respective hammer bases corresponding to the respective lines of typing characters, said printing hammers each impacting, when the corresponding coil means is energized, a selective one of the characters facing the printing paper through the printing paper by an impacting force applied thereto through the corresponding friction disc, wheel member, first gear, second gear and hammer base in the order named; and means for urging said printing hammers away from said type bases, respectively. 